A Kufi (koo fee) is a hat traditionallly worn by muslims, it is made of a lace like material and sits atop ones head. To "get on" ones kufi means to be putting them under pressure, or straining them in some capacity. To trash talk someone, or call them out for what they are doing wrong.

He was out there talking major shit to that nigga, your boy was getting on a niggas kufi.